The present invention relates to a microwave oven and, more particularly, to a variable cooking mode selector for controlling a magnetron output in a microwave oven.
A control system has been proposed, which intermittently enables a magnetron employed in a microwave oven for varying a mean output level in accordance with variations of a repetition rate of magnetron energization.
In a conventional control system of the prior art, a contactless switching system made of a semiconductor circuit, or a complicated cam mechanism is employed to perform the intermittent switching operation. However, both the contactless switching system and the cam mechanism of the prior art are so complicated that a simple control system is highly desirable.
A simplified cam mechanism for varying the mean output level of the magnetron is proposed in my copending application, VARIABLE COOKING MODE SELECTOR IN A MICROWAVE OVEN, Ser. No. 767,149, filed Feb. 9, 1977. In the system disclosed in the above-mentioned application Ser. No. 767,149, the mean output level of the magnetron is selectable at four different levels but cannot be continuously varied.
A system for continuously varying the mean output level of the magnetron is disclosed in U.S. Pat. No. 3,995,133 entitled "VARIABLE POWER CONTROL FOR MICROWAVE OVEN" issued on Nov. 30, 1976. However, the system disclosed in U.S. Pat. No. 3,995,133 is very complicated.
Accordingly, an object of the present invention is to provide a microwave oven, wherein a mean output level of a magnetron employed in the microwave oven is selectable at a desired value.
Another object of the present invention is to provide a variable cooking mode selector of a simple construction for continuously varying a mean output level of a magnetron employed in a microwave oven.
Still another object of the present invention is to provide a switching assembly of a simple construction for intermittently energizing a magnetron employed in a microwave oven.
Yet another object of the present invention is to provide a novel cam structure for intermittently energizing a magnetron employed in a microwave oven.
Other objects and further scope of applicablility of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustraiton only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a cylindrically shaped cam member having a longer radius section and a shorter radius section is driven to rotate at a constant velocity about its axis. The ratio of the longer radius section to the shorter radius section is gradually increased along the axis of the cylindrically shaped cam member.
A contact member associated with an actuator of the normally open switch is disposed in such a manner that the contact member is always brought into contact with the periphery of the cylindrically shaped cam member. The normally open switch is closed when the contact member is brought into contact with the longer radius section of the cylindrically shaped cam member during the rotation of the cylindrically shaped cam member, and is opened when the contact member is brought into contact with the shorter radius section of the cylindrically shaped cam member during the rotation of the cylindrically shaped cam member.
A magnetron power supply circuit is correlated with the normally open switch so as to intermittently energize a magnetron employed in a microwave oven in response to the opening and closing of the normally open switch.
The location of the contact member is shifted along the axis of the cylindrically shaped cam member through the use of a suitable selector, whereby the ratio of the ON period to the OFF period of the normally open switch is selected at a desired value. Therefore, the mean output level of the magnetron employed in the microwave oven is continuously varied in response to the location of the contact member.